The present invention relates to a process for handling particulate materials at elevated pressure. More particularly, the present invention relates to a process for handling inert particulate material such as carbon black at elevated pressure such as in a gas-phase, fluidized-bed polymerization (e.g., of an ethylene-propylene or ethylene-propylene-diene rubber, polybutadiene, or polyisoprene).
Recently, the production of sticky polymers such as, for example, ethylene-propylene-diene rubbers has been conducted in a gas phase polymerization process. These processes typically employ an inert particulate material which forms a coating on the sticky polymer; serves to maintain the bed of forming polymer in a fluidized state; and prevents agglomeration.
Commercially, inert particulate materials are available in the form of beads or pellets which are too large to adequately coat and maintain the forming polymer in a fluidized state. Therefore, in order for these inert particulate materials to perform effectively, they have to be reduced to a smaller particle size before being fed to the gas-phase, fluidized-bed reactor. This small particle size material, such as carbon black fluff, is difficult to feed in a controlled manner because it has a tendency to pack and/or bridge. In particular, carbon black fluff sets up into a hardened mass when it is pressurized with gas to elevated pressures. This elevated pressure may typically be about 25 psig. Physical agitation of the packed inert particulate material such as carbon black fluff is impractical for use with a commercial-size polymerization reactor.
Accordingly, there is a need for a method of feeding small particles of particulate material such as, for example, inert particulate material, especially carbon black fluff, to a gas-phase, fluidized-bed polymerization under elevated pressure in a controllable manner.
The present invention provides a process comprising the steps of: (1) pressurizing a particulate material in bead or pellet form in at least one vessel to an elevated pressure with a first gas, (2) reducing the particulate material to a fine consistency under the elevated pressure, (3) conveying the fine consistency particulate material into a receiving vessel.
In a preferred embodiment the invention is a process comprising the steps of: (1) pressurizing a particulate material in bead or pellet form in a vessel to an elevated pressure with a first gas, (2) conveying the particulate material under elevated pressure into a polymerization reaction system in a manner that mechanically breaks the beads or pellets to a fine consistency, and, optionally (3) employing a second gas to convey said fine-consistency particulate material into the reaction zone of the polymerization system.
In another preferred embodiment, there is provided an improved process comprising the steps of (1) conveying the particulate material in bead or pellet form in at least one vessel at low pressure to one or more small (xe2x80x9cshotxe2x80x9d) pressure vessels where it is pressurized to an elevated pressure with an inert gas or monomer, (2) conveying particulate material under said elevated pressure into a polymerization reactor under conditions of sufficient shear between the beads or pellets and the wall of the conveying device such that the beads or pellets are reduced to a fine consistency or xe2x80x9cfluffxe2x80x9d.
In still a further embodiment there is provided in a process for the polymerization of at least one olefinic monomer in the presence of a catalyst under polymerization conditions in the presence of a particulate material, the improvement which comprises the steps of: (1) pressurizing said particulate material in bead or pellet form in at least one vessel to an elevated pressure with a first gas, (2) conveying the particulate material under said elevated pressure into a grinding device, (3) grinding the particulate material to a fine consistency at said elevated pressure, (4) passing a second gas through said grinding device and thereby conveying said fine-consistency particulate material into a polymerization reactor.